Returns or sets the number of periods (or units on a scatter chart) that the trendline extends forward. Read/write Long.
This example sets the number of units that the trendline extends forward and backward. The example should be run on a 2-D column chart that contains a single series with a trendline.
With myChart.SeriesCollection(1).Trendlines(1)
.Forward = 5
.Backward = .5
End With